This K01 application presents a career development plan for research on posttraumatic stress disorder (PTSD) and comorbid substance use disorder (SUD) and serious mental illness (SMI) for individuals involved in the criminal justice system. There is an increasing demand for programs that can effectively address the needs of mentally ill persons who cycle in and out of the criminal justice system, yet little is known about the comprehensive needs of these clients and how to intervene in a way that balances costs and benefits. A growing body of research identifies PTSD and comorbid SUD as highly prevalent yet largely overlooked problems among people with SMI served in the mental health system. Although limited research suggests a higher prevalence of traumatic victimization and SUD in jail populations, research exploring the prevalence of PTSD/SUD and its relationship to other mental health and criminal justice outcomes is currently lacking. The proposed training plan complements the candidate's background in mental health services for PTSD by providing hew skills in core areas of criminal justice systems and populations, randomized clinical trials, economic and advanced statistical analysis, and substance abuse. The research plan will use these newly acquired skills to address policy-relevant questions regarding the treatment of individuals with dual disorders in the criminal justice system. Two studies will be undertaken: (1) assessing the prevalence of PTSD/SUD among people with SMI in criminal justice diversion programs and testing whether PTSD is a primary mechanism responsible for the association between trauma, substance abuse, and SMI;and (2) carrying out a pilot feasibility study in a local jail diversion program using a modified CBT treatment for PTSD/SUD with mentally ill offenders. Based on findings from these two preliminary studies a R01 application will be developed to test the treatment-effectiveness and cost-effectiveness of an integrated intervention in a large sample, randomized study design with individuals diverted from jail who have comorbid PTSD/SUD. These training and research experiences will provide the necessary foundation for career success as an independent investigator exploring PTSD and dual disorders at the interface of the mental health and criminal justice systems.